Minneapolis , Minnesota -LRB- CNN -RRB- -- For 13-year-old Arrianna Merritt , the words mother and hero go hand in hand .

Three years ago Sunday Arrianna watched her mother Kim Dahl drive a school bus loaded with children across the Mississippi River when the bridge began to buckle up and down . Thirteen people were killed in the bridge collapse in Minneapolis , Minnesota . What Arrianna remembers most was the choice her mother made that day after the bus became tilted upward on a steep incline .

`` Either you let us free fall -- or you hold that brake to the ground and you stay where you are . '' Dahl held the brake with her foot until she could reach for the parking brake .

Millions of viewers saw the jaw-dropping images of the school bus as it teetered on the edge of a broken stretch of highway , with nothing but a guard rail separating it from a deadly fall . Arrianna sat in the bus with her brother , 50 other children and eight adults .

The bus `` went up , and then it went down , '' Dahl recalls , adding it soon turned into free fall and she was `` hanging on for dear life . '' `` I thought ` this is it , ' I 'm not getting out , and I 'm going to die . ''

The new 35W bridge : Is it the safest in America ?

With the parking brake on , Dahl kept the bus in place while everyone made it out the rear emergency door safely . Arrianna , 10 at the time , and her then-5-year-old brother David , were the last ones and had refused to get off with the others .

`` We did n't want to leave our mom , '' David , now 8 , remembers .

`` I 'm like ` get your butts off the bus , ' '' Dahl said . They eventually did .

Dahl says she managed to break free herself after a jolt on the bridge seemed to release her seatbelt , which had been stuck .

Since that day , those on the bridge and their loved ones have never been the same . This particular mother-daughter pair say they 've always had a tight bond but Arrianna says she and her mother have grown even closer since their ordeal .

`` We 've always been close , but I think after the accident we got closer because we shared the same experience and we know what its like , '' Arrianna said .

The physical reminders of that day often overshadow the emotional ones .

`` It does hurt to see my mom in pain because she cant do the things that she used to love to do . ''

Dahl broke her back in the fall and that 's been the primary cause of complications since .

`` It 's like a new me that I 'm living with , '' Dahl said . `` It 's almost like your freedom is taken away ... I ca n't go grocery shopping by myself because I ca n't lift the milk up and put it in the cart . ''

`` My kids and my husband -- I could n't ask for a better family , '' Dahl said . `` I mean my kids step up and do a lot of the work that I ca n't do or help me do things that I ca n't do . They 're pretty good about saying ` yea . ' ''

`` I do n't know if life will ever be normal like it was before July of '07 and prior , but we 've made the best for it , '' said Dave Dahl . `` We 've adjusted our lives , we 've changed our lifestyles . But we 've just got to be positive . ''

Dave Dahl reminds himself that things could have been worse . `` Our family unit here in this house is five people , '' he says . `` Within an instant it could have been two . ''

Arrianna in particular has taken on a number of duties , like cleaning the bathrooms and doing the laundry , that she says has taught her how to be `` a grown-up . ''

`` Most of the time when my mom is in the hospital or getting surgeries , I have to step in and be the surrogate mother to my younger siblings , '' Arrianna explains . The family also includes another daughter , Brianna , age 11 .

`` And my dad is working a lot of the time so he kind of does n't have much time . ''

`` It kind of teaches me to grow up some and how to be a grownup and what it 's like . ''

She adds it can get difficult once in awhile , but these days she simply reminds herself who she 's doing it for .

`` Now I kind of understand why I have to stand in and why sometimes I have to be the adult . ''

Kim Dahl deals with PTSD , as well , and still sees a therapist twice a month . And while Arrianna no longer has therapy sessions of her own , occasionally she still struggles . Kim Dahl is among 122 victims and their families who 've filed suit against URS Corp. , an engineering and construction firm hired by Minnesota DOT to conduct engineering analysis on the bridge before it collapsed . A federal investigative report blamed the collapse on support plates that were too thin , and increased weight on the bridge from construction equipment . The amount of punitive damages plaintiffs are seeking against URS is `` hard to say , '' said Dahl 's attorney Bill Harper , who estimated it could be as much as $ 100 million . `` URS was hired by the state to make sure the integrity of the bridge was safe for the public , '' Harper said Wednesday . `` They did not do what they promised to do -- and as a result -- that bridge collapsed . '' Attorneys for URS said the company 's `` work was unrelated to the causes of the bridge collapse . ... URS did not design the bridge , was never asked to verify the bridge 's original design , and did not know the bridge 's original design was defective . '' Hennepin County District Judge Deborah Hedlund is expected to rule on punitive damages by mid-October . Painful reminders

On Tuesday Kim Dahl and Arrianna visited the site of the collapse -- where the new I-35 West bridge stands . The sound of a jackhammer in the distance is enough to remind Arrianna of the construction noise taking place on the bridge at the time of the accident . It brings her to tears .

Thankfully mom is nearby .

`` She is kind of like my counselor because she listens , '' Arrianna said . She no longer needs a therapist , but it 's these rare moments when mom comes in handy .

And occasionally , Arrianna says , their roles are reversed . She recalls hearing her mother sometimes say things about how life would be easier if none of this had ever happened .

Arrianna 's advice ?

`` You need to move on , and you need to be strong and live your life to the fullest . ''

Those are words the family is living by . Kim Dahl has had to give up what her husband Dave Dahl would call the `` wilder motor sports , '' and the five of them have taken on a new hobby : road trips .

Kim Dahl says she 'll never be able to drive a bus again -- something she misses more than anything . She had the same bus routes for years and knew the kids and their parents well .

But the family camper may be the next best thing . So far , they 've made it as far as Florida to the east and Colorado to the west .

`` My mom could never afford it ... we never went anywhere , '' Kim Dahl recalls of her childhood . `` And we went on -LSB- our -RSB- first trip and it was just awesome . To learn stuff and to see stuff was just amazing . ''

As Dave Dahl describes it , there 's `` no stress , there 's no itinerary , nothing , we just go . ''

`` Wherever we get is where we get , '' he adds . `` We kind of have a goal of where we like to be in the end . ''

Given the path Kim Dahl and her loved ones have traveled since 2007 , that phrase could be the family motto too .

@highlight

Mom helped save 52 kids , eight adults after '07 Minneapolis bridge collapse

@highlight

Ordeal of surviving the collapse of 1,900-foot bridge changed her family forever

@highlight

Mother , daughter bonded tightly , returning to the bridge site 3 years later

@highlight

Mother 's health issues from the collapse forced daughter `` to be a grownup ''